Unfortunately app has stopped. What does java.lang.NullPointerException mean?

Unfortunately app has stopped. What does java.lang.NullPointerException mean?

When I press run an my app I get this message. CAnanyone help me please? I
am posting my LogCat here:
09-10 21:40:54.102: E/AndroidRuntime(11894): FATAL EXCEPTION: main
09-10 21:40:54.102: E/AndroidRuntime(11894): java.lang.RuntimeException:
Unable to start activity
ComponentInfo{com.example.shoppingapp/com.example.shoppingapp.CurrencyConverter}:
java.lang.NullPointerException
09-10 21:40:54.102: E/AndroidRuntime(11894): at
android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2114)
09-10 21:40:54.102: E/AndroidRuntime(11894): at
android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2139)
09-10 21:40:54.102: E/AndroidRuntime(11894): at
android.app.ActivityThread.access$700(ActivityThread.java:143)
09-10 21:40:54.102: E/AndroidRuntime(11894): at
android.app.ActivityThread$H.handleMessage(ActivityThread.java:1241)
09-10 21:40:54.102: E/AndroidRuntime(11894): at
android.os.Handler.dispatchMessage(Handler.java:99)
09-10 21:40:54.102: E/AndroidRuntime(11894): at
android.os.Looper.loop(Looper.java:137)
09-10 21:40:54.102: E/AndroidRuntime(11894): at
android.app.ActivityThread.main(ActivityThread.java:4963)
09-10 21:40:54.102: E/AndroidRuntime(11894): at
java.lang.reflect.Method.invokeNative(Native Method)
09-10 21:40:54.102: E/AndroidRuntime(11894): at
java.lang.reflect.Method.invoke(Method.java:511)
09-10 21:40:54.102: E/AndroidRuntime(11894): at
com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1038)
09-10 21:40:54.102: E/AndroidRuntime(11894): at
com.android.internal.os.ZygoteInit.main(ZygoteInit.java:805)
09-10 21:40:54.102: E/AndroidRuntime(11894): at
dalvik.system.NativeStart.main(Native Method)
09-10 21:40:54.102: E/AndroidRuntime(11894): Caused by:
java.lang.NullPointerException
09-10 21:40:54.102: E/AndroidRuntime(11894): at
com.example.shoppingapp.CurrencyConverter.onCreate(CurrencyConverter.java:36)
09-10 21:40:54.102: E/AndroidRuntime(11894): at
android.app.Activity.performCreate(Activity.java:5184)
09-10 21:40:54.102: E/AndroidRuntime(11894): at
android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1094)
09-10 21:40:54.102: E/AndroidRuntime(11894): at
android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2078)
09-10 21:40:54.102: E/AndroidRuntime(11894): ... 11 more